Discussion of Ames Laboratory TBD Findings on 

External Dose

 Rev 0

National Institute for Occupational 

Safety and Health 

March 3, 2016 

Thomas P. Tomes 

National Institute for Occupational Safety and Health 

Division of Compensation Analysis and Support 
Discussion of Ames Laboratory TBD Findings on External Dose

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This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

1.0 Introduction

The Ames Laboratory Technical Basis Document (TBD) (ORAUT, 2012) contains external dose 

information used as guidance for dose reconstructions. 

SC&A’s review (SC&A, 2013) of the TBD resulted in several findings that question the values 

or sufficiency of the external dose reconstruction methods in the TBD. This document discusses 

those issues and proposes some changes be made to the TBD. 

Each of SC&A’s findings on external dose are listed below in section 2.0 with a brief response. 

The sections that follow discuss the issues in more detail and present an overview of the methods 

NIOSH proposes to be used in a revised TBD. 

2.0 External Dose Findings

Finding #3: NIOSH’s selection of personnel at the Ames Laboratory Research Reactor 

(ALRR) Facility as the target population is inappropriate and results in dose estimates that are 

not claimant favorable.

Response: This finding concerns ambient external dose. The ambient external dose 

values in the TBD should be eliminated because the currently available data is limited. 

External coworker doses should be used when individual monitoring data is insufficient 

to complete a dose reconstruction. This is discussed in more detail in section 6.0. 

Finding #4: NIOSH’s selection of data from the 1961 survey conducted at the Synchrotron 

Facility defines fenceline dose rates that are 1 to 2 orders of magnitude lower than other 

measurements reported in the survey when beam direction was shifted from a westerly to 

easterly direction.

Response: This comment concerns ambient external doses, which NIOSH is now 

proposing to eliminate from the TBD, as noted above. The much higher dose rates from 

the 1961 survey mentioned by SC&A are dose rates inside the Synchrotron fence when 

the Synchrotron was operating at 60 to 65 MeV. Ambient dose should not be used for 

dose reconstructions for any Synchrotron worker, whether inside or outside the building. 

Finding #5: SC&A concludes that the 1961 survey measurements, which were limited to 

gamma dose rates, were incomplete and may have substantially underestimated total exposure 

by excluding the contribution of particulate radiation. 
Discussion of Ames Laboratory TBD Findings on External Dose

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Response: This finding concerns ambient external doses, which NIOSH is now 

proposing to eliminate from the TBD, as noted above. Coworker data should be used 

when individual dosimeter data is not available. 

Finding #21: SC&A’s concerns about the use of the same surrogate data sources and 

questionable assumptions for deriving external dose for Ames’ workers exposed to uranium 

closely parallel those related to uranium intakes as cited in Findings #10 and #13. 

Response: NIOSH recommends changes to the surrogate dose data in the TBD, as 

discussed in section 5.3. As noted in related Finding #13, SC&A also questions the 

sufficiency of providing multiple building and multiple job category levels of exposure 

for external dose during the uranium production years. Based on review of available 

information on work locations for claimants, job categories, and the nature of work 

evolutions at the Ames facilities during the uranium production years of 1942 through 

1945, NIOSH is proposing a simpler approach that should be favorable to claimants and 

that can be implemented consistently. 

Finding #22: Given the availability of highly credible and site-specific data for deriving external 

doses from thorium exposure, NIOSH’s decision to exclude said exposure/doses is not justified. 

Response: In the designation for the SEC class added via petition SEC-00185, the 

Secretary of Health and Human Services determined certain external doses cannot be 

reconstructed with sufficient accuracy from 1942 through 1954 (Sebelius, 2011). SC&A

suggested radiation surveys taken in March 1952 are sufficient for estimating doses from 

1942 – 1952. NIOSH does not consider those results sufficient to characterize external 

radiation exposures from thorium production, as indicated in the Evaluation Report for 

SEC-00038 (NIOSH, 2006). 

Additional review by NIOSH for this finding indicates some limited gamma dose results 

are available from film badges in late 1952, but these were reportedly for some 

Synchrotron workers. Regular dosimetry for beta-gamma exposures began at Ames 

Laboratory in 1953. Thorium production ended in April 1953. 

NIOSH has compiled dosimeter results and considers the available beta-gamma 

dosimetry data sufficient to use for unmonitored doses starting in 1953. Some neutron 

dosimeter data are available starting in 1954, and NIOSH intends to use that data to 

assign unmonitored dose for workers potentially exposed to neutrons starting in 1954. 

NIOSH intends to clarify the use of coworker data in updated instructions in the next 

revision of the TBD. 
Discussion of Ames Laboratory TBD Findings on External Dose

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

3.0 SEC Feasibility Determinations

Classes of Ames Laboratory workers have been added to the Special Exposure Cohort (SEC) for 

1942 through 1970 based on insufficient data to fully reconstruct certain internal and external 

doses. Information on those determinations are provided in section 1.3 of the TBD. 

The Designation Findings for the most recent SEC class, added via petition SEC-00185, includes 

a determination that certain external doses cannot be reconstructed from 1942 through 1954 

(Sebelius, 2011). NIOSH previously determined it only has sufficient information to estimate 

beta-gamma dose from exposure to uranium in all years, beta-gamma dose from other sources 

starting in 1953, and neutron dose starting in 1954 (NIOSH, 2006). 

4.0 General Approach to External Dose Reconstruction at Ames Laboratory

There are no dosimetry data available at Ames until 1952. The available 1952 data is not 

sufficient for dose reconstructions. NIOSH will consider any individual dose data that is 

available for a claim. 

External dose from potential exposure to uranium, as specified in the TBD, will be included in 

dose reconstructions. Section 5 of this document discusses changes recommended to the TBD for 

reconstruction of external dose from uranium in response to the comments received from SC&A. 

NIOSH has a database of Ames dosimetry data that can be used to estimate unmonitored beta 

and gamma doses starting in 1953 and unmonitored neutron doses starting in 1954. These data 

will be applied to unmonitored workers, as appropriate. Table 6-7 of the TBD provides the 

coworker data. This paper also proposes to use the coworker data to bound ambient dose. 

5.0 External Dose Reconstruction from Uranium Operations

Coworker data is sufficient to reconstruct unmonitored beta gamma doses starting in 1953. In 

this document, surrogate data from another site has been used to estimate uranium dose from 

1942 through 1952. The methods presented herein differ from those in the Ames TBD, based on 

more appropriate data available in the Electro Metallurgical Company TBD (NIOSH, 2015). 

The current Ames TBD surrogate uranium data approach is summarized in section 5.2 and the 

newly proposed surrogate data is presented in section 5.3. 

5.1 Ames Uranium Operations 

Iowa State College produced uranium metal from 1942 through 1945. The initial early 1942 

Iowa State College contract was for developmental work. It involved experimental work with 
Discussion of Ames Laboratory TBD Findings on External Dose

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small quantities of uranium compounds to develop metal reduction methods. This experimental 

work led to a production operation in the latter part of 1942. The production operation involved 

reducing UF4 to metal “biscuits”, or ingots, then recasting them into derbies. Ames also had an 

operation to recover and recast scrap uranium metal turnings generated at other sites. 

The buildings involved with uranium production were the Chemistry Building, Physical 

Chemistry Annex I (Annex I), and Physical Chemistry Annex II (Annex II). The production 

operations were done in Annex I and Annex II, which were temporary production facilities 

established at Ames while industry established more permanent production facilities. The 

Chemistry Building work was more limited to early development work; however, uranium metal 

for the Metallurgical Laboratory was produced in that building in 1942. Iowa State College’s 

uranium production operation continued until the latter part of 1945. Additional information on 

the Ames uranium production work can be found in NIOSH Response to SC&A Review of the 

Ames Site Profile Regarding Uranium Internal Exposures (Ellis and Tomes, 2015). 

5.2 Current Ames TBD Surrogate Uranium Dose

The current version of the Ames TBD provides prescriptive annual external doses in Tables 6-4, 

6-5, and 6-6 for workers in the Chemistry Building, Annex I, and Annex II, respectively. 

The annual doses provided in TBD Tables 6-4 and 6-5 for the Chemistry Building and Annex I 

were based on dose from refining uranium. The TBD references the Mallinckrodt site Technical 

Basis Document (ORAUT, 2010) and The Industrial Hygiene of Uranium Refining (Christofano 

and Harris, 1960) as the source of the data. The Table 6-6 dose values for Annex II are based on 

dose rates provided in Battelle-TBD-6000 (Battelle, 2011) that are applicable to working with 

cast uranium metal. 

The doses provided in Tables 6-4 and 6-5 for the Chemistry Building and Annex I are higher 

than those for Annex II to allow for exposure to uranium progeny on the surface of freshly cast 

metal (references indicate all the casting work was done either in the Chemistry Building or in 

Annex I). The reduction and recasting furnace work at Ames are the processes for which dose 

rates could be higher than for work with cast uranium metal work or for exposure to UF4. The 

potentially higher dose is attributed primarily to beta radiation from U-238 progeny on the 

surface of freshly cast metal (Battelle, 2011, p. 21). 

The Christifano and Harris paper reported monitoring results from uranium facilities in the late 

1940s and the 1950s. Airborne radioactivity results were the principle subject of the study, but 

some external radiation doses were provided. Most of the external doses provided were from 

facilities that processed ores that had significant gamma dose from radium. None of the provided 

external doses in that reference were from purified UF4 or uranium metal reduction and recasting

operations; therefore, that reference provides no specific doses for the type of uranium operation 
Discussion of Ames Laboratory TBD Findings on External Dose

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at Ames. It also provides no dose rates on the specific type of uranium scrap recovery operations 

at Ames. 

The Ames TBD also cites the Mallinckrodt TBD for dose rates from refining uranium; however, 

it is not clear how the doses in Tables 6-4 and 6-5 were determined. Although some of the work 

at Mallinckrodt was similar to the work at Ames, there were multiple production processes at 

Mallinckrodt that would not be applicable to Ames workers. Therefore, other sources of data is 

now considered for the Ames TBD. The use of Batelle-TBD-6000 is considered appropriate for 

exposure to uranium metal; however, more appropriate surrogate data is discussed in section 5.3. 

Each of the three TBD external dose tables for the uranium facilities have somewhat different 

dose values and each have five levels of exposure based on job categories. SC&A questioned 

the sufficiency of the surrogate dose data in Finding #21; they also provided additional detail on 

application of the surrogate data in finding #13. Finding #13 questioned the multiple job 

categories and said scaling of uranium doses based on facility and job function is without 

technical support. NIOSH agrees there is insufficient information to support the multiple dose 

levels based on job descriptions. Changes are proposed below. 

5.3 Proposed Surrogate Uranium Dose 

NIOSH does not believe work process and job assignments were established well enough at Iowa 

State College in 1942 through 1945 to provide facility-specific and job-based doses. It was also 

reported in references that due to the urgency of the program Ames sent workers wherever they 

were needed regardless of their assigned job. NIOSH plans to remove the TBD’s distinction of a 

lower dose potential for Annex II workers. The three building-specific dose models will be 

replaced in favor of a single facility dose model. Annual doses will be provided that will be 

applicable to two categories of workers: those who potentially worked with uranium or in the 

contaminated facilities and those who were not likely to work in the production areas or with the 

material. The latter, lower exposed, category of workers are assumed to have made entries in the 

uranium facilities and received significant incidental exposure. 

NIOSH recently issued a Technical Basis Document that includes an evaluation of coworker 

external doses at the Electro Metallurgical Company (Electro Met). The coworker data is from 

dosimeters worn by workers from June 1948 to September 1949. The Electro Met data is more 

representative of potential exposures to uranium production workers at Ames than what is 

currently provided in the Ames TBD. The Electro Met coworker data is also somewhat higher 

than the doses in Battelle-TBD-6000, which the TBD currently uses for Annex II workers

exposed to uranium metal. NIOSH considers the Electro Met data the best currently available 

data to estimate dose for Ames uranium workers who are not compensated via the SEC class.
Discussion of Ames Laboratory TBD Findings on External Dose

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Electro Met’s uranium production facility used the “Ames process” to reduce UF4 to uranium 

metal ingots, which were then recast into derbies and shipped to other sites. The Ames process 

was developed during the uranium production period at Ames. Some of the early development 

work at Ames involved other experimental methods, but by August 1942, the basic Ames 

method was established. That method was improved and evolved into the methods used for the 

bulk of the production work at Ames, and it was the method used by Electro Met. The Ames 

process development work was largely concerned with how to construct the reduction “bomb” 

and how to obtain larger and more pure ingots. Although some minor process differences are 

noted during the development work at Ames, the Electro Met data likely overestimates average 

exposures at Ames during the early development period when smaller quantities were processed. 

Additional evaluation on the surrogate data use criteria is included as Attachment A of this 

document. 

The Electro Met TBD Table 7 provides an annual photon dose of 4.403 rem based on the 95th

percentile of the weekly dosimeter results. The 95th percentile will be assigned to “Operators”; 

Operator dose will be applicable to anyone involved with research, production, labor, 

maintenance, or any non-administrative type of work. Some workers had little potential for 

exposure. A lower exposure category for ”Administrative Workers” will be used and assigned 

the Electro Met median annual dose of 1.356 rem; that level of dose will allow for intermittent 

exposure in the production areas under the presumption that they could have intermittent 

exposure for a significant amount of time. The Administrative Worker category should be 

applied to secretaries, security personnel, managers, or other office personnel. Attachment B has 

information on the job descriptions from NOCTS for claimants with employment in the 1942 

through 1952 period. 

Beta doses will be assigned similar to the Electro Met model at ten times the gamma dose to

allow for higher potential beta dose from reduction and remelting. Extremity dose in the Electro 

Met TBD is based on TBD-6000 values, as that is the best available data. Hand and forearm dose 

is provided only for the Operator category. 

The proposed new doses for Ames for 1942 through 1945 are summarized in Table 2.
Discussion of Ames Laboratory TBD Findings on External Dose

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Table 2: Uranium Production Period Annual Doses, 1942 - 1945 

Operators

Whole body, photons: 4.403 rem

Non-penetrating, skin of whole body: 44.03 rad

Non-penetrating, hand and forearms: 276 rad

Administrative Workers

Whole body, photons: 1.356 rem

Non-penetrating, skin of whole body: 13.56 rem

1. The annual dose should be prorated for partial years, as applicable, and applied in 

IREP as the median value of a lognormal distribution with a geometric standard 

deviation of 3.

Although Ames’ uranium production operations ended by the end of 1945, other operations 

continued in Annex I and Annex II, notably thorium production before construction of Wilhelm 

Hall was completed. Prior to 1953 it is not feasible for NIOSH to reconstruct dose from 

radioisotopes other than uranium; however, NIOSH can provide a bounding estimate of potential 

dose from uranium in the post production years. 

Although uranium production was turned over to industry, some uranium research and 

developmental work may have continued at Ames after 1945. That work may have involved 

some metal casting work, or at least there was some limited potential exposure to uranium metal. 

This is suggested by records of shipments of relatively small quantities of uranium metal from 

Ames in the years after the war (a few hundred pounds compared to many tons produced during 

the war). The median dose from the production years should bound the external dose to workers 

potentially exposed to uranium during 1946 through 1952 (Ames coworker data is available 

starting in 1953). Uranium exposures are presumed to have occurred in the Chemistry Building, 

Annex I, or Annex II, the three facilities associated with earlier uranium developmental and 

production work. 

Records for claimants indicate that not all Ames workers worked in any of the three uranium 

facilities, or had jobs that involved working with radioactive material. For those workers an 

estimate of whole body dose from contamination is made to allow for any occasional entrance 

into the uranium contaminated facilities. 

External dose from uranium contamination is derived from the median Type S uranium intake of 

6,932 pCi/day (Ellis and Tomes, 2015). This production era calendar day intake rate was derived 

from Ames bioassay data during uranium operations. An air concentration correlating to that 

intake rate was estimated by assuming an annual inhalation volume of 2,400 m3

. This results in 

an air concentration of 2,340 dpm/m3. An estimate of surface contamination was made using the 

methods specified in Battelle-TBD-6000 section 3.4.2. These assumptions provide a 

contamination level of 4.55 x 106

 dpm/m2. The dose rate factors from Battelle-TBD-6000, 
Discussion of Ames Laboratory TBD Findings on External Dose

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Table 3.10, were then used to estimate a photon dose of 0.004 rem per year and a beta dose of 

0.042 rem per year based on a 48 hour work-week. 

Doses for the Ames post uranium production period are provided in Table 3. 

Table 3 Uranium Post Production Period Annual Doses, 1946-1952 

Uranium Facility Workers

Whole body, photons: 1.356 rem

Non-penetrating, skin of whole body: 13.56 rem

Other Workers

Whole body, photons: 0.004 rem

Non-penetrating, skin of whole body 0.042 rem

1. “Uranium Facility Workers” dose is to be applied dose to any worker in the 

Chemistry Building, Annex I, or Annex II, or to workers whose work locations are 

unknown. “Other Workers” dose is for all other workers, or for workers who had 

only occasional entries in those three facilities. 

2. The annual dose should be prorated for partial years, as applicable, and applied in 

IREP as a constant. 

6.0 Ambient External Dose

The Ames TBD provides annual ambient external doses for the years 1949 through 1977 in 

Table 4-6. Those years span the operational years of the Synchrotron facility and the Ames 

Laboratory Research Reactor (ALRR). NIOSH reviewed comments from SC&A and available 

data and references. The issues and proposed resolutions are discussed below. 

Two sources of ambient dose were considered in the TBD: dose from the Synchrotron and dose 

from the Ames Laboratory Research Reactor (ALRR). TBD Table 4-6 provides 0.025 rem per 

year ambient dose from the Synchrotron for 1949 through 1977 (derived from 1961 radiation

surveys), and it provides 0.001 rem per year ambient dose from the ALRR for 1965 through 

1977 (derived from modeled release of Ar-41). 

SC&A commented on ambient external dose in Findings 3, 4, and 5. Those findings concern the 

target population for the ambient dose calculation in the TBD, interpretation of radiation dose 

rate measurements taken around the Synchrotron Building in 1961, and potential ambient 

exposures from particulate radiation around the Synchrotron. 

In the discussion related to Finding #3, SC&A provided specific comments based on workers 

meeting the definition of ambient dose provided in section 4.0 of the TBD, which defines 

ambient dose as dose received “outside facilities (e.g., buildings)”. Ambient dose, as applied to 

dose reconstruction for Ames Laboratory, needs further clarification. Instructions with Table 4-6 

specify ambient external doses are to be assigned only to unmonitored workers and makes no 
Discussion of Ames Laboratory TBD Findings on External Dose

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distinction of whether a worker was potentially exposed inside a building or outdoors. Although 

some language in the TBD is not clear on the use of ambient dose, the TBD does not limit the 

application of ambient does to people working outside. 

Conversely, the application of coworker dose in lieu of ambient dose is not limited to indoor 

work. TBD section 6.3.1.2 prescribes coworker dose for unmonitored workers who could have 

been intermittently exposed, and makes no distinction whether it was indoor or outdoor 

locations. For example, SC&A’s comment included a scenario of an outdoor maintenance 

worker within the Synchrotron fence. Per the definition in TBD section 4.0 he could have 

ambient exposures, but the TBD did not consider dose rates inside the Synchrotron fence in the 

ambient dose estimates. In that scenario, if NIOSH does not have monitoring records coworker 

dose should be applied whether their tasks were indoors or outdoors. 

For Ames, the ambient external dose should be considered the minimum dose to be assigned to 

an unmonitored worker from exposure to any source on site. The definition in TBD section 4.0 

should be clarified and be consistent with instructions in section 6.3.1.2. That change should 

resolve some of the issues raised by SC&A. However, SC&A also had comments on the TBD’s 

estimate of dose rates at the Synchrotron facility perimeter fence.

The ambient dose from the Synchrotron in TBD Table 4-6 was derived from a subset of the 1961 

radiation measurements at the Synchrotron fence when the beam was on, with the values chosen 

to be applicable to use to derive a dose rate in an eastern direction within the ALRR area and 

adjusted for distance as described in TBD section 4.2. This was chosen as the location of a target 

population because it was the closest routinely occupied area. The selected data and method used 

in the TBD to estimate ambient doses at the Synchrotron boundary are arguable, and there does 

not appear to be a clear resolution to SC&A’s Findings 4 and 5 using the 1961 data. 

The Synchrotron and ALRR were located a couple miles from the main campus. The TBD 

provides no ambient external dose values from radiation that emanated from operations on the 

main campus. Uranium production ended in 1945, and surrogate dose for uranium exposures 

(through 1952) is considered in section 5.3 of this paper, while Ames coworker beta/gamma data 

is available starting in 1953 and neutron data starting in 1954. Thorium production in Wilhelm 

Hall ended in April 1953 (AEC, 1960). Research activities with radioactive materials continued. 

NIOSH currently has insufficient data to estimate ambient or incidental unmonitored dose. 

In lieu of sufficient ambient dose data, 50th percentile coworker dose should be assigned to 

bound ambient dose for unmonitored workers for all years. Thus, all unmonitored workers 

should be assigned either the 50th percentile dose or the 95th percentile coworker dose, as 

specified in TBD section 6.3.1.2. These changes will be included in a TBD revision. 
Discussion of Ames Laboratory TBD Findings on External Dose

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References

AEC, 1960, History of Thorium Metal Production, Ames Laboratory, USAEC, January 25, 1960, 

Ref ID 18832, pages 22-23. 

Battelle, 2011, Site Profiles for Atomic Weapons Employers that Worked Uranium Metals, 

Battelle-TBD-6000, Revision 1, Battelle Pacific Northwest National Division, Richland 

Washington, June. 

Christofano and Harris, 1960, E. Christofano and W. B. Harris, The Industrial Hygiene of 

Uranium Refining, Archives of Environmental Health, volume 1, pp. 438-460, November, 

[SRDB Ref ID 15774]. 

Ellis and Tomes, 2015, NIOSH Response to SC&A Review of the Ames Site Profile Document 

Regarding Uranium Internal Exposures, National Institute for Occupational Safety and Health, 

Division of Compensation Analysis and Support, Cincinnati, Ohio, July 29. 

Fulmer, E. I, History of the Ames Project Under the Manhattan District to December 31, 1946, 

ISC-10, Iowa State College, Ames, Iowa [SRDB Ref ID 18823]. 

MED, c1944, Construction of Electro Metallurgical Company Area Plant, U.S. Army Corps of 

Engineers Completion Report, Tonawanda Area – Manhattan District, c1944 [SRDB Ref ID 

59225]. 

NIOSH, 2006, SEC Petition Evaluation Report, Petition SEC-00038, Rev. 0, Office of 

Compensation Analysis and Support, Cincinnati, OH, April 10. 

NIOSH, 2008, The Use of Data from Other Facilities in the Completion of Dose Reconstructions 

Under the Energy Employees Illness Compensation Program Act, OCAS-IG-004, Office of 

Compensation Analysis and Support, Cincinnati, OH, August 21. 

NIOSH, 2015, Technical Basis Document of the Electro Metallurgical Company, Rev 01, 

Division of Compensation Analysis and Support, Cincinnati, Ohio, September 24, 2015. 

ORAUT, 2010, Basis for Development of an Exposure Matrix for the Mallinckrodt Chemical 

Company St. Louis Downtown Site and the St. Louis Airport Site, St. Louis, Missouri, Oak Ridge 

Associated University Team (ORAUT) Dose Reconstruction Project for NIOSH, ORAUTTKBS-005, Rev 3, November 22. 
Discussion of Ames Laboratory TBD Findings on External Dose

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

ORAUT, 2012, Site Profile for Ames Laboratory, Oak Ridge Associated University Team 

(ORAUT) Dose Reconstruction Project for NIOSH, ORAUT-TKBS-0055, Revision 03, 

January 3. 

SC&A, 2013, Review of the NIOSH Site Profile for the Ames Laboratory, S. Cohen & 

Associates, SCA-TR-SP2013-0044, Vienna, Virginia, August 14. 

Sebelius, 2011, HHS Designation of Additional Members of the Special Exposure Cohort under 

the Energy Employees Occupational Illness Compensation Program Act of 2000, Designating a 

Class of Employees from Ames Laboratory at Iowa State University, Ames, Iowa, October 18. 

Wilhelm, 1960, Development of Uranium Metal Production in America, Journal of Chemical 

Education, vol. 37, pp. 56-68 [Ref ID 18824]. 
Discussion of Ames Laboratory TBD Findings on External Dose

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Attachment A

Evaluation of Surrogate Data Criteria, Ames Laboratory and Electro Metallurgical 

Company

NIOSH evaluated information on the Ames Laboratory and Electro Metallurgical Company 

facilities and operations to see if the Electro Metallurgical data from 1948 through 1949 would 

be representative of doses at Ames during the uranium production work from 1942 through 

1945. The available information was evaluated using the five criteria listed in sections 3.2 

through 3.6 of The Use of Data from Other Facilities in the Completion of Dose Reconstructions 

Under the Energy Employees Illness Compensation Program Act (OCAS-IG-004) (NIOSH, 

2008). 

Source Term

Ames produced 700 tons of virgin uranium metal from thermite reduction of UF4. Ames also 

produced 300 tons of metal that was recovered from uranium turnings (shipped from other sites). 

Electro Metallurgical also received UF4 and did thermite reduction to produce uranium metal 

ingots, recast the ingots into derbies, and then shipped the metal to other sites. This was the same 

source compounds and production sequence used for most of the mass production at Ames, 

although the earliest work at Ames involved experimental methods and different source 

compounds, but in very small quantities compared to the production work. The dose from scrap 

recovery at Ames is bounded by the dose estimates for virgin metal production, thus the scrap 

recovery work is not considered in this surrogate data review.

The initial experimental and developmental work at Ames also involved uranium oxides, but by 

August 1942 Ames had developed the basic process using UF4, initially on a relatively small 

scale, but further development resulted in a continual increase in production rate up to July 1943, 

after which there was a gradual reduction in Ames’ virgin metal production work. This gradual 

reduction in Ames production coincided with the start of operations at Electro Met. Process 

improvements at Ames were made rather quickly with increasingly larger pieces of metal 

produced. These process improvements were incorporated into the Electro Met operation 

(Wilhelm, 1960). 

The coworker dosimetry data at Electro Met was collected from June 1948 to September 1949. 

The average monthly uranium production rate during that time was about 35 ton/month (or 1.2 

ton/day). The peak uranium metal production rate at Ames (2.2 ton/day) was higher than the 

average rate reported for Electro Met (1.2 tons/day), although Ames operated at that peak only 

very briefly. The peak production rate at Electro Metallurgical is not known, so the average is 

the best statistic to compare. The average production rate for Ames is not provided in available 

references, but can be estimated from various reports. Ames produced about 700 tons of virgin 

uranium metal from 1942 through the end of the war. They had produced only about 2 tons 
Discussion of Ames Laboratory TBD Findings on External Dose

Page 14 of 16

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

through November 1942. Production increased rapidly during process improvements in early 

1943 until its peak on July 1, 1943, then gradually declined. Regular production ended in 

November 1944, but they still received about 4 tons of UF4 per month for metal production 

development work until the war ended. To provide an upper bound of the average monthly 

production at Ames it is assumed all 700 tons of virgin metal was produced in the 22 months 

from January 1943 through October 1944. That results in an average production rate at Ames of 

about 32 ton/month, compared to the 35 ton/month for Electro Met (during the time of the 

dosimeter coworker study). 

Both sites received purified UF4. Exposure would have been to U-238, U-234, and U-235 in 

normal uranium ratios. The UF4 had been processed at other sites, so the short-lived Th-234 and 

Pa-234m progeny would have grown in to some degree since separation. The age since 

purification would affect dose rates from the progeny, with the progeny approaching equilibrium 

with U-238 in about 100 days after purification. The production of UF4 and reduction to metal 

during the war was an urgent matter, and UF4 production did not always keep up with metal 

reduction. It is not likely the UF4 processed at Ames had aged more than the material processed 

at Electro Met in 1948. 

Considering the above conditions, and based solely on source term, the average dose rates in the 

Electro Met TBD should overestimate the dose received by Ames workers. 

Facility and Process Similarities

Electro Metallurgical received UF4 and did thermite reduction to produce uranium metal ingots, 

recast the ingots into derbies, and then shipped the metal to other sites. This was the same source 

compounds and production sequence as Ames. Electro Met used the “Ames Process” that was 

developed at Ames before and during production work. However, there were some differences, 

particularly in the early development period at Ames; these differences concerned perfecting 

materials and reduction bomb preparation methods to produce ingots of ever increasing size. 

Initially Ames processed very small amounts. In August 1942 they were processing batches of 

UF4 only up to 200 gm. By September they had perfected the process enough to process 2-3 kg 

UF4. In late September they had several of the “biscuits” and remelted them into an 11 pound 

ingot. 

The actual process used for the reduction “bomb” was not fully developed until March 1943, 

when process improvements were made and Ames switched from calcium to magnesium as the 

reducing agent. After the method was perfected the reduction bombs produced at Ames varied 

but most were made with 6 inch diameter pipes about 3 feet long, which produced a 42 pound 

“biscuit”, although Ames experimented with 10 inch diameter pipes that produced a 125 lb 

biscuit (Wilhelm, 1960). Electro Met produced ingots weighing 110-135 kg (50 – 61 lb) 

(NIOSH, 2015). 
Discussion of Ames Laboratory TBD Findings on External Dose

Page 15 of 16

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

The Electro Metallurgical plant was built to mirror the Ames process and Electro Met engineers 

made trips to Ames in 1942 and 1943 to build their facility to mimic the process. Wilhelm 

reported the process was the same other than a difference in the metal casting equipment, which 

he described in some detail; he also discussed the evolution of changes in the process at AEC 

facilities from 1942 into the 1950s (Wilhelm, 1960). 

Temporal Considerations 

The facility utilized for most of the metal reduction and recasting at Ames (Physical Chemistry 

Annex I) was not designed to be an industrial plant. It was a converted single story frame 

building with additions to accommodate uranium production until industry constructed 

production facilities. Airborne radioactivity and worker internal doses could have been much 

different; however, these differences have more limited effect on external dose. 

The Electro Metallurgical production facility was constructed from 1942 to 1943. Some limited 

operations began in March 1943 during construction, and minor changes to the facility continued 

to be made to incorporate processes and information learned at other facilities (MED, c1944; 

NIOSH, 2015). Based on descriptions and floor plans of the Electro Metallurgical plant, there 

does not appear to be any particular design to limit external doses, and none would be expected 

at that time for the given process and source material. Additionally, NIOSH has found no 

indication of any significant design change at Electro Met from construction in 1943 to the time 

of the dosimeter study in 1949. It is thought the principle difference in external dose potential 

would be the work practices at each facility that may result in some workers being exposed for 

longer periods of time in close proximity to uranium metal and compounds. These uncertainties 

are accounted for by a favorable application of coworker dose. 

Data Evaluation

Section 5 of The Electo Met TBD provides a detailed description of the data and how it was 

evaluated. It addresses detection limits and uncertainty. NIOSH considers it the best available 

data that can be used for Ames Laboratory unmonitored dose from uranium production. 

Review of Bounding Exposure Models 

The Electro Metallurgical TBD annual doses are based on the 95th percentile of all monitored 

workers. Doses are applied as a lognormal distribution. The dose distributions of the various job 

categories were compared to the 95th percentile of the all monitored workers. The median values 

of the higher exposed job categories are reasonably bounded by the 95th percentile, with the 

applied lognormal distribution accounting for the spread of the data. 
Discussion of Ames Laboratory TBD Findings on External Dose

Page 16 of 16

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Attachment B 

Job Titles and Scaling of External Dose from Uranium

As indicated above NIOSH plans to remove the three building-specific dose models for Annex 1, 

Annex 2 and the Chemistry Building and replace them with a single dose model that will be 

applicable to all three uranium facilities. In response to SC&A comments, the five categories of 

worker exposure in the current TBD were reviewed and compared to claimant records to 

determine if a location and task/job based exposure model is practical or can be implemented 

consistently. 

The five uranium job categories in the current Ames TBD are the four categories from BattelleTBD-6000 (Operator, Laborer, Supervisor, and Clerical), plus a fifth category of Researcher. 

The Ames TBD assumed the Researcher received 10% of the operator dose. Based on a review 

of job titles, a large percentage of the claims could be in the Researcher category. Table B1

shows all job position/titles for Ames claims in NOCTS with employment from 1942 through 

1945. NOCTS contained fifteen claims with employment during the uranium production period. 

Thirteen of the fifteen claims had a job description in NOCTS. There are two claims with no job 

title listed in NOCTS. Additional information in the claims files indicate the two workers were

[REDACTED]. 

This review of claimant records and Ames process references indicates there is not sufficient 

supporting information to estimate scaled doses to various types of production workers or 

research personnel. 

Table B1

Job Titles for Claims with Employment Starting in 1945 or Earlier*

[REDACTED]

Table B2 shows all job positions/titles for Ames claims in NOCTS with employment in 1942 

through 1952. 

Table B2

Job Titles for Claims with Employment Starting in 1952 or Earlier

[REDACTED]